need help with checking piston to valve clearance (clay method)
09-01-2010, 06:58 PM
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need help with checking piston to valve clearance (clay method) I have tried searching and didn't find any good how to threads. Can some one please post a good link? MIght also need a good fly cutting how to 
. Clay method seems like it would be easy.
. Clay method seems like it would be easy. Last edited by bigfatls6; 09-01-2010 at 07:33 PM.
09-02-2010, 12:53 PM
#4
While clay sounds "caveman" compared to a dial indicator, its actually just as effective and can offer some insight that a dial indicator does not.....specifically how much radial clearance you have around the valve.
You may have a country mile in depth but without also using clay to check, may not realize the valve was a blond hair away from one or both sides of the valve relief in the piston which could cause mechanical interference under operating conditions when pistons and valves are slightly moving and flexing, especially at higher RPM (ever see a valve dance and move around when viewing a video made on the Spintron....you would be afraid to get on your car if you did....LOL)
I like clay for backing up the data my dial indicator provides me with and I really like clay for seeing exactly where the valve lands in the pocket. Both are key pieces of information necessary when building any motor, but especially a high performance engine.
However (big "however" here guys), the key to using either method, which gets missed by so many rookie engine builders (and not so rookie engine builders as well), is you must use a solid lifter or a welded hydraulic (so it acts solid) when your testing piston to valve and when your degreeing the cam as well for that matter. I have a set of Crane solid roller lifters that I use specifically for all my engine mock up. I cant tell you how many people drop the ball on this using the hydraulic lifters that either came with the engine or they planned on using. The plunger collapses a bit under the load of the test spring and .068 P to V is really .018 or worse and they find out after the fact when they have tagged and bent a few valves or potentially scrapped their engine with an even uglier outcome.
Sorry to go off a bit in a slightly different direction with this reply but is all related to the same procedure and its good advice that Im sure potenially might save some of you reading this alot of financial hardship down the road.
-Tony
You may have a country mile in depth but without also using clay to check, may not realize the valve was a blond hair away from one or both sides of the valve relief in the piston which could cause mechanical interference under operating conditions when pistons and valves are slightly moving and flexing, especially at higher RPM (ever see a valve dance and move around when viewing a video made on the Spintron....you would be afraid to get on your car if you did....LOL)
I like clay for backing up the data my dial indicator provides me with and I really like clay for seeing exactly where the valve lands in the pocket. Both are key pieces of information necessary when building any motor, but especially a high performance engine.
However (big "however" here guys), the key to using either method, which gets missed by so many rookie engine builders (and not so rookie engine builders as well), is you must use a solid lifter or a welded hydraulic (so it acts solid) when your testing piston to valve and when your degreeing the cam as well for that matter. I have a set of Crane solid roller lifters that I use specifically for all my engine mock up. I cant tell you how many people drop the ball on this using the hydraulic lifters that either came with the engine or they planned on using. The plunger collapses a bit under the load of the test spring and .068 P to V is really .018 or worse and they find out after the fact when they have tagged and bent a few valves or potentially scrapped their engine with an even uglier outcome.
Sorry to go off a bit in a slightly different direction with this reply but is all related to the same procedure and its good advice that Im sure potenially might save some of you reading this alot of financial hardship down the road.
-Tony
01-02-2011, 02:36 AM
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Ok I'll try to explain.
This can only be done accurately with a solid lifter as Tony stated above. For those of you using hydros this will only be able to be done during the mock up assembly of the fresh motor.
The "solid" lifter can usually be made for test purposes out of the existing hydro. Dissemble a lifter, remove the spring and check valve off of the bottom of the plunger and find a steel ball bearing/little washers combo that will "take up" nearly all the internal travel and still allow the use of the plunger/cup that the pushrod fits in. Reassemble your now nearly solid "test" lifter dry. (should do two of these with the LS type motor).
Normal first mock up (checking clearances) often is as follows (on engine stand):
Crank installed with intended use bearings, lubed.
1 piston/rod assembly installed, bearing lubed, at least one of the compression rings installed.
Cam, t chain, 1 pair of lifters installed. Cam timing needs to be at final use setting if you have an adjustable set up.
Put a thin layer of modeling clay maybe 1/4 thick on the suspected valve contact area. Use real modeling clay not play-doh. The piston needs to be super clean with nothing on its surface (dry). You sort of push the clay into the piston top, really work it in to give it the greatest "purchase" on the piston top. You are trying to keep the clay stuck on the piston.
Prep target chamber valves with some kind of release agent on them. I've used vegetable oil before. A light skimming is all that is needed. Heads/valves need to be completely clean before applying release agent(waxing the valves might work as well). You are trying to keep the clay off of the valves
Install head with an already compressed head gaket of the same thickness/brand that you intend to use. In this case you can re-use your old head bolts and there is no need to do the 90 degree steps. torque them to 30 and stop.
Install pushrods into your modified/solid lifters and the rocker arms.
Adjust rockers to 0 lash on the base circle of cam! Very important! Can't get it to 0 lash?
Your doomed!
You have to be able to make the entire valvetrain path solid with no clearance but also no pre-load to get this measurement accurately.
You should start this process at TDC compression of the cylinder your are checking.
Turn crankshaft 2 complete revolutions smoothly in a single continuous motion.
Remove head.
Heres where this measurement's accuracy depends more on the inspector than on the measuring device utilized.
The valves will have left impressions in the clay (and hopefully not pulled it off of the piston). What you have to measure is the thickness of the clay at its thinnest point. The problem comes from not being able to access the thinnest portion in cross section easily. If you cut the clay it changes the thickness. Lots of folks say "use a micrometer as a depth gauge". Usually the base of the micrometer is not shaped like the valve impression and doesn't fit for measuring worth a flip.
I end up gauging clay thickness using a tooth pick; the business end blunted flat with a sandpaper. Carefully inserting it and marking it with a super sharp pencil right at the surface of the clay. Remove and measure the marked distance. Then I'll carefully slice the clay with a razor and directly measuring it as well. Practice makes perfect in this case.
Have true flat top pistons? (most LS engines do) This makes measuring this easier. Lots easier
Have valve reliefs already? Makes it more difficult to determine but also more important for exactly what Tony posted before. There is no other way than this for verifing valve travel compared to valve reliefs that I can think of. You end up looking at a real life "patterning" of what you have in your application compared to what the piston maker thought you would need. Piston makers are human too and your application might be just enough different that it makes a difference.
On an engine taken to the ragged edge of performance all of the valves and pistons will need to be checked.
If your set-up shows plenty of clearance on one chamber, both in radial and total depth, then doing the other 7 might not be as important.
Different folks have different opinions on how much clearance is required. If you have more that .120 exhaust and .100 intake your probably in the clear.
True solid mechanical roller cams might do this test at proper valve lash adjustment. It would depend on the engine builder. Using 0 lash for checking with a mechanical cam gives you the lashes worth of "wiggle" room so I use 0 lash on everything. Others might disagree....
Sorry for the length. Hard for me to really decribe it quicker.
By the way, I am a noob the the LS series, not to wrenching but definite noob regarding specific LS applications. The lifter modification at the start might not be able to be performed on a LS hydro. I've never had a LS lifter to look at or take apart although I'm planning to rectify this failure on my part shortly.
I could see where if you were doing this test or degreeing cams on a regular basis you would keep a sacrifical set of solid lifters around to be used as "tools".
Hope this helped.
This can only be done accurately with a solid lifter as Tony stated above. For those of you using hydros this will only be able to be done during the mock up assembly of the fresh motor.
The "solid" lifter can usually be made for test purposes out of the existing hydro. Dissemble a lifter, remove the spring and check valve off of the bottom of the plunger and find a steel ball bearing/little washers combo that will "take up" nearly all the internal travel and still allow the use of the plunger/cup that the pushrod fits in. Reassemble your now nearly solid "test" lifter dry. (should do two of these with the LS type motor).
Normal first mock up (checking clearances) often is as follows (on engine stand):
Crank installed with intended use bearings, lubed.
1 piston/rod assembly installed, bearing lubed, at least one of the compression rings installed.
Cam, t chain, 1 pair of lifters installed. Cam timing needs to be at final use setting if you have an adjustable set up.
Put a thin layer of modeling clay maybe 1/4 thick on the suspected valve contact area. Use real modeling clay not play-doh. The piston needs to be super clean with nothing on its surface (dry). You sort of push the clay into the piston top, really work it in to give it the greatest "purchase" on the piston top. You are trying to keep the clay stuck on the piston.
Prep target chamber valves with some kind of release agent on them. I've used vegetable oil before. A light skimming is all that is needed. Heads/valves need to be completely clean before applying release agent(waxing the valves might work as well). You are trying to keep the clay off of the valves
Install head with an already compressed head gaket of the same thickness/brand that you intend to use. In this case you can re-use your old head bolts and there is no need to do the 90 degree steps. torque them to 30 and stop.
Install pushrods into your modified/solid lifters and the rocker arms.
Adjust rockers to 0 lash on the base circle of cam! Very important! Can't get it to 0 lash?
Your doomed!
You have to be able to make the entire valvetrain path solid with no clearance but also no pre-load to get this measurement accurately.
You should start this process at TDC compression of the cylinder your are checking.
Turn crankshaft 2 complete revolutions smoothly in a single continuous motion.
Remove head.
Heres where this measurement's accuracy depends more on the inspector than on the measuring device utilized.
The valves will have left impressions in the clay (and hopefully not pulled it off of the piston). What you have to measure is the thickness of the clay at its thinnest point. The problem comes from not being able to access the thinnest portion in cross section easily. If you cut the clay it changes the thickness. Lots of folks say "use a micrometer as a depth gauge". Usually the base of the micrometer is not shaped like the valve impression and doesn't fit for measuring worth a flip.
I end up gauging clay thickness using a tooth pick; the business end blunted flat with a sandpaper. Carefully inserting it and marking it with a super sharp pencil right at the surface of the clay. Remove and measure the marked distance. Then I'll carefully slice the clay with a razor and directly measuring it as well. Practice makes perfect in this case.
Have true flat top pistons? (most LS engines do) This makes measuring this easier. Lots easier
Have valve reliefs already? Makes it more difficult to determine but also more important for exactly what Tony posted before. There is no other way than this for verifing valve travel compared to valve reliefs that I can think of. You end up looking at a real life "patterning" of what you have in your application compared to what the piston maker thought you would need. Piston makers are human too and your application might be just enough different that it makes a difference.
On an engine taken to the ragged edge of performance all of the valves and pistons will need to be checked.
If your set-up shows plenty of clearance on one chamber, both in radial and total depth, then doing the other 7 might not be as important.
Different folks have different opinions on how much clearance is required. If you have more that .120 exhaust and .100 intake your probably in the clear.
True solid mechanical roller cams might do this test at proper valve lash adjustment. It would depend on the engine builder. Using 0 lash for checking with a mechanical cam gives you the lashes worth of "wiggle" room so I use 0 lash on everything. Others might disagree....
Sorry for the length. Hard for me to really decribe it quicker.
By the way, I am a noob the the LS series, not to wrenching but definite noob regarding specific LS applications. The lifter modification at the start might not be able to be performed on a LS hydro. I've never had a LS lifter to look at or take apart although I'm planning to rectify this failure on my part shortly.
I could see where if you were doing this test or degreeing cams on a regular basis you would keep a sacrifical set of solid lifters around to be used as "tools".
Hope this helped.
01-02-2011, 02:59 AM
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This statement is correct in that it's a whole lot easier to get an accurate total depth measurement as you are reading a single gauge, not trying to measure a thin piece of flexible clay.
Both methods have merits.
The dial indicator method would need a different (probably equally long) write up. Its screw up point is knowing exactly at what degree of crankshaft rotation the valves are closest to the pistons. This is harder to determine than you might imagine.
With true flat top pistons the dial indicator test is completely acceptable, maybe better than the clay method.
It is also faster and far less work.
On a solid lifter application the dial indicator method can be done without having to pull the heads. It can be done in chassis on a "dirty" engine if the previous builder degreed and marked the balancer accordingly.
Both methods have merits.
The dial indicator method would need a different (probably equally long) write up. Its screw up point is knowing exactly at what degree of crankshaft rotation the valves are closest to the pistons. This is harder to determine than you might imagine.
With true flat top pistons the dial indicator test is completely acceptable, maybe better than the clay method.
It is also faster and far less work.
On a solid lifter application the dial indicator method can be done without having to pull the heads. It can be done in chassis on a "dirty" engine if the previous builder degreed and marked the balancer accordingly.
